• Cab signal suppression

  • For topics on Class I and II passenger and freight operations more general in nature and not specifically related to a specific railroad with its own forum.
For topics on Class I and II passenger and freight operations more general in nature and not specifically related to a specific railroad with its own forum.

Moderator: Jeff Smith

  by MattW
How do the different cab signaling systems get suppressed? For instance, I understood the procedure to be any cab signal reduction requires placing the brake handle in suppression (which is a large pipe reduction, 20lbs?) until the speed is below the newly required speed. Is this accurate? If so, how is that proper train handling when on a non-cab-signaled route, the engineer might use the dynamics instead of the air?
  by Wayside
If the track is only equipped with automatic cab signals (ACS) without a form of speed control system being involved, it is not necessary to go to suppression. The operator merely acknowledges the signal restriction and brakes accordingly to comply with the speed required for compliance. If the signal changes to a less favorable than clear, and the operator fails to acknowledge the signal in the time allowed, then a suppression application is the only way to recover from a penalty situation, and thus requiring a full stop. Speed control changes all of that, in that if speed does not reduce sufficiently, a penalty will occur, which can only be taken care of with a suppression application and a full stop.

And, yes, a full stop penalty is not conducive to good train handling on a long, heavy freight train.
  by MattW
But what about systems with speed control? If the signal drops from clear to approach medium, how is that acknowledged?
  by Wayside
MattW wrote:But what about systems with speed control? If the signal drops from clear to approach medium, how is that acknowledged?
The same time as acknowledging the cab signal drop, by activating the acknowledging pedal or button device, but with the added requirement of getting speed down to 30 mph within the allowed time to do so.
  by WhartonAndNorthern
A few questions about cab signal systems:

1.) Is a penalty brake a "service" reduction or is the train put into emergency?
2.) Before ACSES and PTC, which railroads had speed enforcement as part of their cab signalling system? I know about the LIRR.
3.) So on systems without speed control, is pressing a button sufficient to avoid penalty or does the system look for some movement of the brake handle/reduction in train line pressure?

Are there any good resources out there for learning about cab signal design and implementation? I'm an electrical and computer engineer with extensive embedded systems development background. I'm interested in learning about signal insertion and interruption in welded rail, SIPs etc.. I'd also like to know how the steam-era cab signal receivers were designed. Some combination of relays and maybe vacuum tubes. I'm especially interested in how they distinguished between the pulse rates. Any design I can come up with in my head would require a lot of relays.
  by Wayside
1. A penalty application is a service rate of reduction.
2. I can't answer that one.
3. An automatic cab signal system without some kind kind of speed control only requires acknowledgement of the signal change within a specific amount of time. This is accomplished by pressing a button, moving a lever, or stepping on a pedal.
  by ExCon90
2. The PRR had it; I don't know about others.
  by WhartonAndNorthern
Thank you for replying ExCon90 and Wayside!
  by 57A26
C&NW on it's Chicago - Council Bluffs main line, and IC on part of it's Iowa main line had Automatic Train Control. UP still uses the CNW ATC, although PTC is replacing it. The CNW system only has two aspects, clear and restricting. Before UP added CTC, most areas didn't have wayside signals other than interlocking locations. Only cab signals.

Above 40mph if the cab signal went to restricting, the engr has 6 seconds to acknowledge the change and place the brake valve in suppression. Suppression is a full service application. So is the penalty application, but the penalty also opens the PC switch which will cause the engines to go to idle. Forcing one to stop to reset the PCS. Before the monster trains came along, one could do a running release from suppression. ATC restricting enforces a top speed of 22 mph, but above 17 mph you get a constant audible warning.

Below 40mph you have 6 seconds to acknowledge the change and 70 seconds to get below 23 mph. While running at restricted speed the system requires an acknowledgement every few minutes.
  by Engineer Spike
As a result of the Chase, MD Ricky Gates incident, Amtrak had Locomotive Speed Limiter. Metro North uses it too. If a downgrade of signals is encountered, then the audible whistle sounds. The engineer must acknowledge the change. The limiter has a count down timer, just like PTC. The quicker you slow down, the timer adds back time. A penalty happens if the signal change is not acknowledged, or the train doesn’t slow down fast enough before the timer times out.
  by Wayside
Prior to Conrail's departure from electric ops on the NEC, electric motors were equipped with speed control. In subsequent operations, up until the Chase incident, cab signals were pretty much just indicators in the cab that demanded acknowledgement of signal drops from "clear" in order to avoid penalty applications. Amtrak supervision were pretty much stunned when they realized Conrail had been operating all those years with ACS alone. :(
  by tubalcain
On the PRR. PC passenger trains we simply cut the brake valve out, put the valve in suppression and acknowledged the cab signal change. The train brakes would not set up unless there was a big leak. If you wanted a little brake you just cut the valve in for a short time. It worked great! Of course we did not have the tattletale (recorder) strapped to us. The Star at Chase, MD was not Gates but brakeman Cromwell. He gave the testimony that the prosecution team wanted for immunity. Gates did time- Cromwell walked. Or so I remember.